WINE-SEARCHER -- An end might be in sight to the long-running war between vineyard owners and their greatest enemy – phylloxera.
The genome of the phylloxera, an insect that caused plagues that devastated European vines in the 19th Century and has remained a potent threat ever since has been mapped by an international team involving researchers Miquel Barberà and David Martínez, from the Institute for Integrative Systems Biology (I2SysBio), center of the University of Valencia. The study was published in the journal BMC Biology.
The work opens the way for changing how viticulturists combat the pest and it could eventually lead to resistant rootstocks, eliminating the need for costly grafting.
"Growers currently have to graft roots to make their plants viable," Paul Nabity, an assistant professor of plant-insect ecology at UC Riverside, told the Growing Produce website. "A lot of money and effort could be saved with pest-resistant rootstocks."
The work confirmed that the pest originated from North America, most likely from wild populations located along the upper reaches of the Mississippi River. The study's conclusions have helped reconstruct the biological invasion that unleashed deadly plagues on European vineyards in the 19th Century, as well as advancing strategies to improve productivity in viticulture.
The sequencing of the new genome has been promoted by the international consortium, featuring more than 70 experts from eight countries around the world, created in 2011 and led by the French National Institute of Agriculture (INRAE).
The work of the I2SysBio experts has focused on the annotation of a series of genes related to the pest's circadian rhythm and to the induction of the sexual phase.
"These are genes involved in photoreception, as well as candidate genes to trigger an adequate response to certain environmental changes that produce modifications in the life cycle," says David Martínez, researcher at I2SysBio and one of the authors of the article. Both Martínez and Miquel Barberà have dedicated their last years of research to identifying and characterizing genes related to the aphids' biological cycle, and contributed 10 years ago to the sequencing and publication of the Acyrthosiphon pisum genome.
"Phylloxeras are insects related to aphids and share a complex life cycle with them, with which they can share molecular mechanisms of control of their life cycles."
The phylloxera (Daktulosphaira vitifoliae, also known as Phylloxera vastatrix) is a hemipteran insect of the Phylloxeridae family that feeds on the sap that it obtains from the roots of vines. First described in 1854 by the entomologist Asa Fitch in the United States, it caused some initial outbreaks of infection in France in 1863, before it was definitively identified in 1868 by Bazille, Planchon and Sahut, members of the Hérault Agricultural Society in Montpellier.
The busy vine trade between the United States and Europe was the most likely accidental point of entry the accidental for the insect, which inexorably spread throughout the continent, changing forever the face of the wine industry. Vineyards in Britain were the first to notice the infestation and it first appeared in France in the Rhône Valley in 1863, whence it spread to the rest of the country and beyond. By 1889, Bordeaux's production was down by around 70 percent.
Since then, most European vines have been grafted onto American rootstocks, since they are resistant to the aphid. Only small pockets of ungrafted vines remain around the world, mostly in regions with soil types that are inimical to the pest.
Analysis of the genomic sequence of the phylloxera nuclear DNA reveals the existence of the largest gene family ever identified in a genome – with around 2700 genes, when 200 are rarely exceeded – which would represent 10 percent of the insect's genome.
These genes, probably essential for interactions between the phylloxera and vines, encode the small secreted proteins –known as effectors – that could be involved in deactivating the plant's basic defenses. In the vines of the region of origin, the coevolution between plant and pest would have enabled the resistance of the vines to the insect. In contrast, vines grown in Europe did not have a defense system adapted to ward off the threat of the new plague and its lethal cocktail of effectors.
The published work also confirms that the phylloxera that invaded Europe comes from the Vitis riparia species, a wild type of American vine.
From an applied perspective, the genomic information from the new study will enable genetic improvement in viticulture practice. Thus, a better understanding of the evolution and mechanisms of action of the new family of effector genes will help design strategies that block their action through interventions on the plant or parasite.
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